Payment models for the display of online advertising with a search service, (hereinafter, a search engine) include pay-per-click, which obliges advertisers to pay search engines a fee each time a user clicks on an ad displayed on a search page or search result page or any widget or web content displaying advertisements. This type of payment model is susceptible to click fraud, which is constituted by clicks made with the intention of costing the search engine or the advertiser money without providing anything of value in return (i.e. clicks made with the intention of distorting the market). The distributed nature of the Internet and the relative anonymity of browsers make detecting click fraud difficult.
An alternative payment method which avoids the problem of click fraud provides that the search engine receive a fee for each user conversion. A conversion occurs each time a user engages in a transaction with a merchant after reaching the merchant's website by clicking on an online advertisement. A merchant may have many conversion types such as, but not limited to, purchases of goods, services, registrations, or subscriptions. A credit card or other type of transaction may serve as proof that an authentic conversion has occurred and thereby reduce the risk of fraud. However, one difficulty with the pay-for-conversion method may be that the interests of the advertiser/merchant and the search engine do not align.